Fuel and ignition control



Feb. 1, 1949. F. J. HAHN FUEL AND IGNITION CONTROL Filed June 25, 1945 Patented Feb. l, 1949 FUEL AND IGNITION CON '.IROL

Frank J. Hahn, Kansas City, Mo., assignor to United Aircraft Corporation, East Hartford, Conn., acorporation of Delaware Application June 25, 1945, Serial No. 601,439 Claims. (Cl. 12S-117) This invention relates to the control of fuel and ignition systems for engines, particularly aircraft engines, and represents an improvement on the invention disclosed and claimed in Jarvis application Serial No. 601,438, now Patent No. 2,453,093, issued November 2, 1948, filed concurrently herewith, assigned to applicants assignee.

An object of this invention is to provide improved means automatically effective only under predetermined conditions for regulating the mixture strength of an engine.

Another object is to provide improved means for correlating the ignition timing and the mixture strength of an engine.

A further object is to provide a. novel control apparatus, particularly for internal combustion aircraft engines.

Other objects and advantages will be apparent from the speciiication and claims, and from the accompanying drawing which illustrates what is now considered to be a preferred embodiment of the invention.

In the drawing, Fig. l is a schematic view showing a fuel and .ignition control apparatus constructed according to the teaching of this invention.

Fig. 2 shows schematically fuel-air ratio curves such as may be obtained with the control apparatus of Fig. 1. Y

'Ihe embodiment of the invention shown in the drawing is particularly adapted for use with aircraft engines having engine driven superchargers, but it is to be understood that the invention is not limited -to such use.

In the Jarvis application, referred to above, the I ignition timing and mixture strength of an engine may be controlled so that when the timing is varied the mixture strength, or thev fuel-air weight ratio of the engine charge, will be varied accordingly.

By the present invention, the mixture strength can be automatically varied in accordance with spark advance under certain engine charging conditions but may be independent of spark advance under other engine charging conditions.

Referring to the embodiment of the invention selected for illustration in the drawings, a radial aircraft engine having air-cooled cylinders, one of which is shown at I1, is supplied with charging fluid (air or 'air and fuel) through induction pipes, one of which is shown at I6, by a main stage supercharger impeller I2 mounted in a supercharger or blower case, a. portion of which is shown at yIII. The impeller is splined at I3 to a shaft I5 driven in a known manner by the ento applicants assignee.

Intake air is supplied to the supercharger inlet or thro I4 by a manifold 22 connected either directly to a scoop or ram positioned in the free airstream flowing over the aircraft or to the outlet of an auxiliary supercharger stage. The rate of flow b` weight of intake air, and therefore engine poner output, is controlled by throttle 24.

Air passing to the engine is measured by carburetor metering section 2t comprising main venturi 30, auxiliary venturi and impact tubes 36, lwhich cooperate to produce throat and scoop pressures in chambers 40 and 38, respectively.

'Ehese pressures, as corrected for variations in density by altitude compensator 32, are admitted to chambers 21, 29 on opposite sides of air diaphragm 28. The resultant force exerted by the diaphragm on fuel flow regulating valve 52 is a function of the rate of flow by weight of intake lair and urges the valve toward open position.

Fuel is supplied to valve 52 by pump 46 from tank 42 through line 41 and strainer 50. A vapor trap including oat valve 48 may be provided to eliminate gases from the liquid fuel,` which is preferably gasoline.

Fuel in an amount controlled by valve 52 flows through unmetered fuel chamber 54 and-line 56 to the fuel control body or metering iet section 5B. After being metered in control body 5,8, the fuel passes through the metered fuel line 68 to the fuel discharge valve I and then into the fuel spinner |54 which sprays it into the air entering the vaned passages of impeller I2.

A fuel diaphragm 64 separates the unmetered fuel chamber 54 from a chamber 62, subjectedv by line to the metered fuel pressure on the downstream side of the metering jets in the control 58. The resultant force exerted by this diaphragm on fuel valve 52 is dependent upon the fuel pressure drop across the metering jets, and urges the valve toward closed position. Fuel and air diaphragms 64, 28 and fuel valve 52 act to maintain a pressure drop across the metering jets vbetween the unmetered and metered lines 56, 68

which is proportional to the compensated air pressure drop between the throat chamber 40 and i the scoop chamber 38, thus regulating the rate Y of flow by weight of fuel to the engine in pre- Serial No. 492,423, filed June 26, 1943, now Patent No. 2,400,307, issued May 14, 1.946, assigned determined ratio to the rate of flow by weight of engine intake air, throughout the engine operating range.

This fuel-air ratio may be varied by controlling the jets in the fuel control body 68. The basic fuel-air ratio throughout the engine operating range is established by the main or cruise jet 66 which is continuously open. In addition to the flow through this Jet, fuel may also flow from the unmetered Jet chamber |66 through the economizer jet l into the chamber l0 and then through the auto-rich Jet 'i6 into the metered jet chamber |6'l, when the auto-rich valve 'l'i is open as shown in Fig. 1. Jet 'i6 has a greater restriction than Jet l0. Therefore, assuming valve 00 to be closed, the mixture is enriched by an amount determined substantially .by the size of jet 76 when valve il is open.

It is desirable under high engine` power output conditions to provide additional enrichment or higher mixture strengths to prevent detonation, and for other purposes. This is accomplished by economizer valve 00 operated by diaphragm 00 subjected to metered `fuel pressure through passage 65 and unmetered fuel pressure through line 66. When the fuel pressure drop becomes suillciently high, valve 60 is opened against the force of spring 00 to provide additional fuel in an amount determined by the value of the fuel pressure drop, the rate of spring 06 and the contour of valve 80, up to a maximum quantity determined by the size .of economizer jet l0, which imposes. a limit on the maximum flow permitted through both valve 60 and jet i6. Fuel enrichment occurs regardless of whether or not the carburetor is in the auto-rich position in which valve ll is open, or in the auto-lean position in which valve lll closes the opening i6 and thereby shuts off the flow of fuel through iet i6. For the moment, flow of fuel through iet "i6 by way of line 002 will be disregarded.

Idle valve iii, linked in a known manner with the throttle 20, is moved to a metering position, in which it restricts the flow from the end of unmetered fuel line 66 and thereby controls the mixture strength, when the throttle is closed and the engine is idling. When the throttle is open, idle valve |0| has no appreciable effect on the mixture strength.

According to the present invention, the above described fuel control apparatus, which is more fully disclosed in Palmer application Serial No. 529,104, filed April 1, 1944, assigned to applicants assignee, is modified and correlated with the engine ignition control apparatus as follows.

An extra lean metering jet 60|, which has a greater restriction than jet 'i6 and which is controlled by a two-position auto-lean valve unit 400, is supplied with fuel by line 102 from charnber 0|. When valve Tl is open, fuel may `flow directly from jet 'l0 and chamber 0i to chamber |51. When valve 'l'l is closed, fuel may flow through jet 'land from chamber 0| only by way of line 402, jet 00| and line 404, to the metered fuel line 68 and thence to the engine. Such flow through the extra lean jet 40| will be terminated by the closing of fuel valve 406. Flow through jet 40| will also terminate when valve 'i'l is moved to open position, because then there will be no pressure drop between the chamber 8| and the metered fuel chamber |51, or the metered fuel line 68. Because under such circumstances there is no pressure drop across jet 40|, there will be no flow therethrough regardless of whether valve 406 is open or closed. Thus. jet 40| and valve 006 are disabled, or rendered ineffective to change the fuel-air ratio, when the engine is operated in the rich mixture setting, or under "auto-rich" conditions.

Valve 606 is biased to closed position by a spring 209 and is opened by a predetermined pressure difference between the unmetered and metered fuel lines 56, 60. The stem of valve 406 is attached to the valve actuating diaphragm |06, which cooperates with the partitions M2', i 0 to form fluidtight chambers on opposite sides of the diaphragm. These chambers are connected to lines 68, 66 by passages 2 i0, 2| i, respectively. Diaphragm |06 actuates the fuel valve 606 and alsoY actuates the by-pass or bleed valve |00 of the ignition system. Valve |90 is held in closed position by spring T. This spring is preferably considerably weaker than the diaphragm spring 209 and serves merely to hold the stern of valve |90 in abutment with the diaphragm. When the pressure difference between fuel-lines 60, 00 becomes sufficiently large, diaphragm |06 overcomes the force of spring 209 and moves upwardly to lift fuel valve 006 from its seat. The diaphragm in its upward movement also contacts the stem of valve |90 and opens this valve against the force of spring 201. Seals (or sealing diaphragms) may be provided if desired at the places where the stems of valves |00, (|06 pass through the partitions M2', M0'.

The engine ignition system comprises magnetos i0', i6' which supply ignition current at timed intervals to spark plugs il' of the engine cylinders il. The magnetos are driven from the engine crankshaft by gear trains including magneto drive gears |00, ||0 in a manner more fully disclosed in Jarvis application Serial No. 481,114, filed March 30, 1943, now Patent No. 2,380,967, issued August 7, 1945, to which reference is made 40 for a more complete disclosure of the basic ignition system referred to herein.

For changing the timing of the magnetos, or the time at which ignition current is supplied to the spark plugs with respect to piston position, the magneto gear trains are each provided with bevel idler gears |06, |06 mounted on cages |00 rotatably supported on the magneto shafts |00, to which gears |00, ||0 are fixed. Cages |08 are connected by arms |66, |66 to a cross bar or link |32 attached to the piston |20 of a servomotor |0I. When pressure fluid such as oil is admitted to one or the other of cylinders |26, |20 of the servomotor the piston |20 will be reciprocated to move link |32 and retard or advance the ignition timing. A spring 30 biases piston |26 to retard position.

Servomotor |0| is controlled by a spark advance operating unit |40 including a servo valve |62 having lands |60, |60 which control the admittance of oil under pressure from the supply line |52 to the lines |58, |60 respectively attached to cylinders |20, |26. Drains |50, |56' are provided for relieving pressure in one cylinder as pressure fluid is admitted to the other.

Valve |62 is actuated by diaphragm |12 subjected to the pressure difference between fluid lines |14, |16, which are respectively connected through restriction to the blower outlet and through restriction 200 to the blower inlet. Thus the chamber portion |10 of the spark advance operating unit is divided bydiaphragm |12 into two iluid tight chambers connected to blower throat and blower'rim.

A spring |18 maintains valve |62 in its downward or retard position, determined by the stop |03. When the force exerted by the fluid pressures on diaphragm |12 is sumcient to overcome the force of spring |16, valve |62 is moved upwardly toits advance position. determined by the abutment of the stop |05 against chamber |70.

, Under some conditions it isdesirable to maintain the sparkretarded even when the supercharger pressure rise is sufficiently high to hold valve |62 in its upper or advance position. For this purpose by-pass valves |60 and 50| are provided.l When either ci' these valves is opened, the effect is to bleed or by-pass air from the blower rim line |14 to the blower throat linel |10. Restrictions |98, 200 are made of lsuc'h value in relation to the size of valves |90, 50| that the opening of either of these valves will approximately equalize the pressure in lines |14, |16,

thereby disabling the ignition timing `mechanism, or rendering it ineffective to advance the spark, by causing the pressures on opposite sides of the diaphragm in chamber to become substantially equalized and enabling spring |10 to maintain or return valve |62 to the retard position.

By-pass valve |90 of the spark advance ccnt'rol unit 202 is controlled by fuel head diaphragm |06. The force exerted by,this diaphragm on the valve is determined by the fuel pressure drop which is in turn determined by the rate of flow by weight of engine' intake air. Consequently diaphragm |66 will open valve |60 against the force of springs 209, 201 when intake, airflow (and engine power output) reaches a predetermined value. Fuel valve 006 will of course be opened and closed simultaneously with ignition valve |90.

By-pass valve 50| in the mixture control E00 is actuated by handle 502. Whenthe handle is moved to change the mixture setting of the carburetor, shaft 5N, fixed thereto, is rotated to angularly adjust yoke 003 connected to valve lever 005, thereby shifting valve 11 to close or open the port 19. Movement of shaft 0M also angularly shifts a cam bit, keyed tothe shaft, to close or open bleed valve 50| against the force of spring 501 by means of bell crank E00, fulcrumed at 5I0. The levers and cam are so arranged that whenever handle 602 is in the auto-rich position valves 71 and 50| are both open and when the handle is in auto-lean position valves 11 and 50| are both closed. A bleed or by-pass is established between lines |14, |16 through pipes 504, 506 'when valve 50| is open.

Operation As the throttle 24 is moved from idle position to the full open position the rate of intake airflow increases and the mixture strength and ignition timing are varied, for example as shown in Fig. 2.

size of jets 66 and 16. The fuel-air ratio is then maintained substantially constant throughout the cruising power range as shown by the horizontal portion of the curve. It is increased by the opening of economizer valve 80 when the power output enters the high or full power range, andthe mixture is gradually enriched, as shown the curve. in accordance with each increase in power output beyond the cruising range. Because of the economizer or limiting jet 10, the fuelair curve iattens out to a substantially constant value, as shown at the extreme upper right hand portion of the curve, when the engine approaches maximum power output.

Under auto-rich mixture conditions valve 50| is open and the pressures in lines |14, |16 are thereby equallzecl, enabling spring |10 to maintain the ignition timing in the normal or retard position regardless of variations in intake airow, power output, or mixture strength.

With an auto-lean mixture setting (valve 11 closed) the fuel-air ratio follows the lower (or auto-lean) curve schematically shown in Fig. 2. The fuel-air ratio decreases as indicated by the sloping line at the left of the curve until the engine power output enters the cruising range. It then remains approximately constant through the range labeled super auto-lean, during which valve 006 is held closed by spring 200. When the rate of intake airow increases to a predetermined value, the fuel metering head be comes sulcient to force diaphragm |66 upwardly, lifting valve 600 to open jet 00| and increase the fuel-air ratio as indicated by the upward step in the curve at the right hand end of the "super auto-lean range. The mixture strength will then again be held constant at this higher value until economizer valve 86 is openedv 'to enrich the mixture in the high power range,

as described above in connection with the auto rich curve.

Valve 50| ls closed when the valve 1l is closed and therefore the ignition timing will be advanced (for instance from 250 B. T. C. normal to 37 B. T. C. cruising spark advance position) when the mixture setting is auto-lean and the 40 supercharger pressure rise becomes large enough to overcome the force of spring |16. An increase in intake airflow (and consequently engine power) also results in an increase in the pressure rise across the supercharger. When the pressure rise reaches a predetermined value (for instance about 3" Hg is suitable in some installations and about 8" Hg for some other installations) diaphragm |12 is forced upwardly to advance the ignition timing.

In Fig. 2 the point at which the blower pressure rise becomes suilicient to compress spring |16 and shift the timing to the advance position has been placed, for illustration, at the beginning of the cruising power range. The point at which the fuel metering head becomes sufficient to i compress the spring 209 has been placed near the upper end oi the cruising power range. With such an arrangement, the engine is operated with the spark retarded in the idling power range, with spark advanced in the "super or extra-lean cruising range (valves |90, 006 closed) and with spark retarded in the lean cruise range (valves |90, 406 open) and the high power range (valve 80 partially or fully open). Thus the ignition timing vand -mixture strength may be automatically regulated, one in accordance with the other, by controls that are automatically rendered effective when the mixture setting is auto lean and `ineffective when the mixture setting is auto-rich.

When the throttle is returned from the full open to the idle position the events described above will occur in reverse order, though preferably at slightly different values of intake alrby the upwardly sloping line at the right of flow. Valves |90 and 406 may be so designed that the pressure differential across them tends to hold them closed, thereby insuring their shift to fully open position 'as soon as they are cracked or partially opened and preventing hunting In other words, the valves may be designed if desired to provide a hysteresis effect, so as to close only when the airflow decreases slightly below the value required to open the valves.

This invention may be used with the water injection apparatus of Palmer application Serial No. 529,104, referred to above, or with fuel injectlon systems in which the fuel is directly injected into the engine combustion chamber or chambers. The invention, of course, is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In combination with an internal combustion engine having a supercharger, a fuel-air ratio control including an intake airow measuring device, an ignition timing control including a supercharger pressure rise actuated device, a pair of fuel metering jets connected in series, and means connected with said intake airflow measuring device and with said supercharger rise actuated device for controlling the flow of fuel through at least one of said jets.

2. A. fuel and ignition control apparatus for engines comprising, device responsive to engine intake airflow for simultaneously varying fuelair ratio and ignition timing, and separate means for rendering said device ineectve to vary either said fuel-air ratio or said ignition timing under predetermined engine charging conditions.

3. In an engine having rich and lean fuel mixture strength settings. means effective in said lean mixture strength setting for varying said fuel mixture strength with the operation. of an engine control device, said means being ineffective to vary said fuel mixture strength in said rich mixture setting.

4. In an engine control apparatus, means for advancing the engine ignition timing, fuel control means operatively associated with said timing means, and means for disabling said timing means and said fuel control means under predetermined engine operating conditions.

5. In an engine having valve means for establishing at least two different substantially constant fuel-air ratios within an intermediate portion of the engine power range, ignition timing means for said engine, and means operatively associated with both said timing means and with said valve means for altering one of said fuel-air ratios within at least a portion of said intermediate power range.

' FRANK J. HAHN.

` REFERENCES CITED The following references are of record in the file of this patent:

NTTED STATES PATENTS Certificate of Correction Patent No. 2,460,383. February 1, 1949. FRANK J. HAHN It is hereby certed that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 4, claim 3, after the Word strength insert simultaneously; and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent OHce.

Signed and sealed this 31st day of May, A. D. 1949.

THOMAS F. MURPHY,

Assistant ommz'ssz'oner of Patents. 

